Longfei Wu

Research Project – Longfei Wu/Jan Philipp Hofmann

The request for sustainable energy is one of the top priorities on the world’s strategic research agenda. Sunlight is an abundant renewable energy source and only 1.2 hours of sunlight correspond to the global energy consumption for a whole year. Photoelectrochemical (PEC) water splitting is an attractive approach to generate hydrogen as a clean chemical fuel from solar energy. Concerning photovoltaics, the unique properties of iron pyrite (FeS2), which include an exceptionally large optica absorption coefficient in the visible region (α>105 cm-1 at hν >1.5 eV), suitable band gap (~0.95 eV), large element abundance, nontoxicity, as well as low material refinement costs, make it a promising candidate material to address the Solar Fuel challenge. The high absorption coefficient of iron pyrite provides a unique opportunity among inorganic materials to incorporate a very thin absorption layer (<100 nm) in a light harvesting device to capture most of the incident solar radiation. However, the material suffers from thermodynamically unstable particle surfaces which are terminated with sulfur dimers caused sulfur vacancies and phase impurities that leads to a high dark current. Therefore, a protection layer is needed to inhibit deleterious reactions. For this project, we will choose MoS2, with a bulk band gap of 1.2 eV, as the protection layer. MoS2 has previously been shown to be a stable and active hydrogen evolution reaction (HER) catalyst. This material is therefore a suitable candidate for combining catalyst and protection layer functionality in only one material.

Pyrite thin films have been synthesized by various techniques, however, pyrite growth by CVD provides a suitable way to obtain phase pure pyrite films with large grain size, less defect sites and a controllable thickness. By changing metal precursors, MoS2 can be grown on top of iron pyrite. The as-obtained multilayer sulfides will be explored as photo cathodes for the solar-driven hydrogen evolution reaction.

For better understanding of the construction of multilayer sulfide films and their photoelectrochemical properties, the project is mainly focused on the following tasks:

Controllable synthesis of iron pyrite films by CVD and evaluation of photovoltaic properties

Layered growth of MoS2 on pyrite films and film composition analysis by XPS